It's ok now Mamba ! I forgot to edit an include call in a file of lexikon directory.

Let's say that at the 1st reading it's not so clear to realize when the changes concerne only the xoopstree file or all other files.
For me, a bit narrow minded, it was confusing and I've had to read 2 or 3 times to be sure what to do !!!

But finally I achieved to make the modification ! Working well ...

Just a question ... 2 in fact ...
- Why is it considered as "dirty" ?
- How to replace the call to xoopstree by a call to xoopsObjectTree ? How to load or implement xoopsObjectTree ? I tried but got an error.

THX !

1) "dirty" was meant here as "quick & dirty", so something that will work, but it's not the best/cleanest solution. But it works, and I am using it all the time when I am converting modules to XOOPS 2.5.6 Admin GUI, because it is faster.

2) Replacing XoopsTree with XoopsObjectTree is not easy, so if you are not comfortable with PHP I would not recommend to do it.

But you can try by following this recommendation from Bumciach